This application is based upon and claims priority of Japanese Patent Application No. 11-300206, filed Oct. 21, 1999, the contents being incorporated therein by reference, and a continuation of PCT/JP00/07355 filed Oct. 20, 2000.
The present invention relates to a method for forming a corrosion preventing layer, on internal surfaces of a metallic tank filled with a fluid such as water, which is effective when applied to the production of a header tank of a radiator.
As is well known, a corrosion preventing layer is a layer constituted by a metal having a larger ionization tendency than that of a base material (a core material) to prevent corrosion of the base material (in this case, a tank main body).
A duplex heat exchanger in which a radiator and a condenser are integrated into a single unit is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 9-152298, and according to the disclosed invention, a header tank of a radiator (hereinafter, referred to as a radiator tank) and a header tank of a condenser (hereinafter, referred to as a condenser tank) are formed through extrusion of aluminum material.
Cooling water or coolant is filled in the radiator tank, and therefore a corrosion preventing layer needs to be formed on internal surfaces of the radiator tank. To this end, in general, an aluminum sheet material having a corrosion preventing layer of zinc formed on the surface thereof is pressed into shapes and the members so pressed into shapes are then joined together through brazing, whereby a header tank is provided which has the corrosion preventing layer formed on the internal surfaces thereof.
AS is described in the aforesaid unexamined patent publication, however, when an attempt is made to produce a radiator tank as an integral unit through extrusion, it is difficult to form a corrosion preventing layer on the internal surfaces of the tank and, therefore, a predetermined corrosion resistance has conventionally been secured by increasing the thickness of the sheet material used for radiator tanks. Since this increases the weight, as well as material cost of radiator tanks, there has been caused a problem that the production cost of radiators so produced is increased.
The present invention was made in view of these situations and an object thereof is to provide a method for forming a corrosion preventing layer on internal surfaces of a tank with ease.
With a view to attaining the object, according to a first aspect of the present invention, disposed within a tank main body (234) is a sacrificial material comprising a metal having a lower electric potential than that of the tank main body (234), so that the sacrificial material is heated in a state in which the same material is surrounded by the tank main body (234).
In this construction, the evaporated sacrificial material is allowed to adhere to internal surfaces of the tank main body (234) relatively uniformly without being radiated out of the tank main body (234). Then, the sacrificial material so adhering to the internal surfaces is dispersed into a metal constituting the tank main body (234), whereby an alloy layer (a corrosion preventing layer) containing the sacrificial material heavily is formed over the internal surface of the tank main body (234).
Consequently, according to the present invention, the relatively uniform corrosion preventing layer can be formed on the internal surfaces of the tank main body (234) with ease.
According to another aspect of the invention, the tank main body (234) comprises at least two parts (233, 235), a sacrificial material constituted by a metal having a lower electric potential than that of the tank main body (234) is disposed on part of an internal surface of at least one of the two parts (233, 235), and the two parts (233, 235) are assembled together so as to surround the sacrificial material so disposed so that the sacrificial material is heated in the surrounded state.
In this construction, the evaporated sacrificial material is allowed to adhere to the internal surfaces of the tank main body (234) relatively uniformly without being radiated out of the tank main body (234). Then, the sacrificial material so adhering to the internal surfaces is dispersed into the metal constituting the tank main body (234), whereby an alloy layer (a corrosion preventing layer) containing the sacrificial material is heavily formed over the internal surface of the tank main body (234).
Consequently, according to the present invention, the relatively uniform corrosion preventing layer can be formed on the internal surfaces of the tank main body (234) with ease.
According to a further aspect of the invention, there are provided a plurality of tubes (211) through which fluid is allowed to flow and metallic header tanks (230) disposed at longitudinal ends of the plurality of tubes (211) for communication therewith. The header tank (230) comprises a tank main body (234) extending in a direction normal to the longitudinal direction of the tubes (211) and caps (236) for closing longitudinal ends of the tank main body (234), and the tank main body (234) and the caps (236) are joined to each other through heat brazing with a sacrificial material comprising a metal having a lower electric potential than that of the tank main body (234) being disposed in the interior of the tank main body (234).
In this construction, as described previously, since a relatively uniform corrosion preventing layer can be formed on the internal surfaces of the tank main body (234), a heat exchanger can be realized which is light in weight as well as low in production cost while the corrosion resistance of the heat exchanger is maintained.
According to a still further aspect of the invention, there are provided a plurality of radiator tubes (211) through which cooling water or coolant is allowed to flow, metallic radiator header tanks (230) disposed at longitudinal ends of the plurality of tubes (211) for communication therewith, a plurality of radiator tubes (111) through which refrigerant is allowed to flow, and metallic radiator header tanks (120) disposed at longitudinal ends of the plurality of radiator tubes (111) for communication therewith. The radiator header tank (230) comprises a radiator tank main body (234) extending in a direction normal to the longitudinal direction of the radiator tubes (211) and radiator caps (236) for closing longitudinal ends of the tank main body (234), and the radiator header tank (120) comprises a radiator tank main body (123) extending in a direction normal to the longitudinal direction of the radiator tubes (111) and radiator caps (124) for closing longitudinal ends of the radiator tank main body (123). Both the tank main bodies (123, 234) are made integral with each other through extrusion or drawing, and furthermore the radiator tank main bodies (123, 234) and the radiator caps (236) are joined to each other through heat brazing with a sacrificial material comprising a metal having a lower electric potential than that of the radiator tank main body (234) being disposed in the interior of the radiator tank main body (234).
In this construction, since a relatively uniform corrosion preventing layer can be formed only in the radiator tank (230) with ease, a duplex heat exchanger can be realized which is light in weight as well as low in production cost while the corrosive resistance of the duplex heat exchanger is maintained.
Note that reference numerals in parentheses after the respective means are one example denoting the relationship between those means and corresponding specific means described in embodiments which will be described later.